Detection and mitigation of interference in a receiver

ABSTRACT

A receiver architecture optimizes receiver performance in the presence of interference. In various embodiments, power estimation circuits are used with variable selectivity to determine the exact nature of the interference and to optimize the performance correspondingly. The variable selectivity is achieved using stages of filtering with progressively narrower bandwidths. Also, the actual method of optimizing the receiver performance is an improvement compared to the traditional techniques in that the gain settings and the baseband filter order (stages to be used) will be optimized based on the nature of the interference as determined by the power detector measurements. For a device such as a cellular phone that operates in a dynamic and changing environment where interference is variable, embodiments advantageously provide the capability to modify the receiver&#39;s operational state depending on the interference.

RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 13/190,161 titled “Detection and Mitigation of Interference in aReceiver” filed Jul. 25, 2011, now U.S. Pat. No. 8,787,507, the entiretyof which is incorporated by reference herein.

FIELD

The present disclosure relates to receiver architectures in acommunications system, and more particularly, some embodiments relate tomethods and apparatuses for detecting and mitigating interference andoptimizing receiver performance.

BACKGROUND

Radio frequency transceivers in cellular systems commonly receive anddecode a desired signal in the presence of interference, which hascommonly required a compromise in receiver performance. For example, inorder to prevent clipping due to interference, several stages of narrowanalog filters are typically found in conventional receiver designs.Such filters add current drain and distort the desired signal, thusdegrading receiver performance. Additionally, the active stages of thereceiver, particularly the radio frequency (RF) stages, are designedwith high levels of linearity so that distortion is minimized in thepresence of interference. This linearity often requires relatively highbias conditions and therefore requires relatively high current drain.

A typical prior art receiver architecture is shown in FIG. 1. Thisarchitecture represents a typical receiver implementation and isdescribed in U.S. Pat. No. 6,498,926 to Ciccarelli et al. Withinreceiver 100, the transmitted RF signal is received by antenna 112,routed through duplexer 114, and provided to low noise amplifier (LNA)116, which amplifies the RF signal and provides the signal to bandpassfilter 118. Bandpass filter 118 filters the signal to remove some of thespurious signals which can cause intermodulation products in thesubsequent stages. The filtered signal is provided to mixer 120, whichdownconverts the signal to an intermediate frequency (IF) with asinusoidal signal from local oscillator 122. The IF signal is providedto bandpass filter 124, which filters spurious signals anddownconversion products prior to the subsequent downconversion stage.The filtered IF signal is provided to variable gain amplifier (VGA) 126,which amplifies the signal with a variable gain to provide an IF signalat the required amplitude. The gain is controlled by a control signalfrom gain control circuit 128. The IF signal is provided to demodulator130, which demodulates the signal in accordance with the modulationformat used at the transmitter (not shown).

For this prior art architecture, the local oscillator signal (LO) iseither tuned to match the radio frequency signal (RF), so that thereceived signal is converted directly to baseband, or it is tuned toconvert the received RF signal to some much lower intermediate frequency(IF) for further filtering. At baseband or IF, the filters are set tothe bandwidth of the particular RF system to receive the desired signaland remove interference.

The architecture in FIG. 1 is designed to receive the desired signal inthe presence of interference. The filter at baseband or IF is set toremove completely any interference, and the RF stage gain and bias areset to receive the signal with interference with minimal distortion.Thus, such a conventional system makes assumptions about the presence ofinterference, which may reduce interference at the expense of receiverperformance when the expected interference is present, but which mayconstitute a wasteful approach when such assumptions are incorrect.

Another prior art receiver architecture is disclosed at FIG. 2 of U.S.Pat. No. 6,498,926 to Ciccarelli et al. In this prior art architecture,post-demodulation quality is used to set the bias conditions andtherefore the linearity of the RF circuits. This prior art approach doesnot address the problem fully because the receiver state is adjustedbased only on the baseband data quality measurement, which might bedegraded for numerous reasons and not just due to interference and/orreduced RF linearity. Also, this architecture does not do anything toreduce the filtering requirement to match the actual interferenceconditions.

Another prior art receiver architecture is disclosed at U.S. Pat. No.6,670,901 to Brueske et al. This prior art architecture includes anon-channel power detector, a wide band power detector, and anoff-channel power detector. The wideband detector and off-channeldetector will indicate if high levels of interference are present andallow adjustment of the receiver bias based on that. This prior artarchitecture suggests using the information from these power detectorsto adjust the dynamic range of several blocks (LNA, mixer, filter,analog-to-digital (A/D) converter, and digital filter). By adjusting thedynamic range and/or bias of these stages, the current drain can beoptimized. However, this prior art approach uses wideband detectionwithout selectivity and therefore is unable to distinguish out-of-bandinterference, i.e., interference that is several channels away, fromnearby interference in the adjacent or nearby channels. Therefore, thearchitecture cannot fully optimize the performance of the receiver.

Since an actual device such as a cellular phone operates in a dynamicand changing environment where interference is variable, it is desirableto be able to modify the receiver's operational state depending on theinterference.

SUMMARY

In some embodiments of the present disclosure, an apparatus includes afirst amplifier configured to amplify an input signal. A mixer iscoupled to the first amplifier. The mixer is configured to mix theamplified input signal outputted by the first amplifier with anoscillator signal, to provide a mixed signal. A first estimation circuitis configured to measure voltage or power of the mixed signal. A firstfilter is configured to filter the mixed signal to pass a first band offrequencies. A second amplifier is configured to amplify an output ofthe first filter. A second estimation circuit is configured to measurevoltage or power at an output of the second amplifier. A second filteris configured to filter the output of the second amplifier to pass asecond band of frequencies narrower than the first band. The first andsecond filters may be baseband filters. A state machine is coupled tothe first and second estimation circuits. The state machine isconfigured to provide feedback to the first and second amplifiers and tothe mixer. The state machine is configured to increase a bias current ofthe first amplifier and/or the mixer, or decrease a gain of the firstamplifier and/or the mixer, or both increase the bias current anddecrease the gain, when the voltage or power measured by the firstestimation circuit is greater than a first predetermined threshold andthe voltage or power measured by the second estimation circuit is lessthan a second predetermined threshold. The state machine is furtherconfigured to decrease a gain of the first amplifier, the secondamplifier, and/or the mixer when the voltage or power measured by thesecond estimation circuit is greater than the second predeterminedthreshold. The apparatus may include a third estimation circuit,configured to measure the voltage or power at an output of the secondfilter, and a third filter, which may be a baseband filter, and whichmay be configured to filter the output of the second filter to pass athird band of frequencies narrower than the second band. The statemachine may be further coupled to the third estimation circuit and maybe further configured to provide feedback to the third filter and tobypass the third filter when the voltage or power measured by the thirdestimation circuit is less than a third predetermined threshold.

In some embodiments of the present disclosure, an apparatus includes afirst amplifier configured to amplify an input signal. A mixer iscoupled to the first amplifier. The mixer is configured to mix theamplified input signal outputted by the first amplifier with anoscillator signal, to provide a mixed signal. A first estimation circuitis configured to measure voltage or power of the mixed signal. A firstfilter is configured to filter the mixed signal to pass a first band offrequencies. A second amplifier is configured to amplify an output ofthe first filter. A second estimation circuit is configured to measurevoltage or power at an output of the second amplifier. A second filteris configured to filter the output of the second amplifier to pass asecond band of frequencies narrower than the first band. A thirdestimation circuit is configured to measure the voltage or power at anoutput of the second filter. A third filter is configured to filter theoutput of the second filter to pass a third band of frequencies narrowerthan the second band. The first, second, and third filters may bebaseband filters. A state machine is coupled to the first, second, andthird estimation circuits. The state machine is configured to providefeedback to the first and second amplifiers, to the first, second, andthird filters, and to the mixer. The state machine is configured tobypass the third filter when the voltage or power measured by the thirdestimation circuit is less than a predetermined threshold.

In some embodiments, an input signal is amplified to provide anamplified input signal, which is mixed with an oscillator signal toprovide a mixed signal. The voltage or power of the mixed signal ismeasured. The mixed signal is filtered at a first filter to pass a firstband of frequencies, to provide a first filtered signal, which isamplified to provide a first amplified signal. The voltage or power ofthe first amplified signal is measured. The first amplified signal isfiltered at a second filter to pass a second band of frequenciesnarrower than the first band, to provide a second filtered signal. Ifthe measured voltage or power of the mixed signal is greater than apredetermined threshold T1 and the measurement at Pdet2 is less than apredetermined threshold T2, then a bias current used for the amplifyingthe input signal, and/or for the mixing may be increased. If themeasured voltage or power of the first amplified signal is greater thanthe predetermined threshold T2, then a gain used for at least one of theamplifying the first filtered signal, the amplifying the input signal,and amplifying the mixed signal may be decreased. The voltage or powerof the second filtered signal may be measured. A third filter may beprovided to filter the second filtered signal, to pass a third band offrequencies narrower than the second band, and to provide a thirdfiltered signal. If the measured voltage or power of the second filteredsignal is less than a predetermined threshold T3, then the third filtermay be bypassed.

In some embodiments, an input signal is amplified to provide anamplified input signal, which is mixed with an oscillator signal toprovide a mixed signal. The voltage or power of the mixed signal ismeasured. The mixed signal is filtered, at a first filter, to pass afirst band of frequencies, to provide a first filtered signal, which isamplified to provide a first amplified signal. The voltage or power ofthe first amplified signal is measured. The first amplified signal isfiltered, at a second filter, to pass a second band of frequenciesnarrower than the first band, to provide a second filtered signal. Ifthe measured voltage or power of the mixed signal is greater than apredetermined threshold T1 and the measurement at Pdet2 is less than apredetermined threshold T2, then a gain used for the amplifying theinput signal and/or the mixing may be decreased. If the measured voltageor power of the first amplified signal is greater than the predeterminedthreshold T2, then a gain used for at least one of the amplifying thefirst filtered signal, the amplifying the input signal, and amplifyingthe mixed signal may be decreased. The voltage or power of the secondfiltered signal may be measured. A third filter may be provided tofilter the second filtered signal, to pass a third band of frequenciesnarrower than the second band, and to provide a third filtered signal.If the measured voltage or power of the second filtered signal is lessthan a predetermined threshold T3, then the third filter may bebypassed.

In some embodiments, an input signal is amplified to provide anamplified input signal, which is mixed with an oscillator signal toprovide a mixed signal. The voltage or power of the mixed signal ismeasured. The mixed signal is filtered, at a first filter, to pass afirst band of frequencies, to provide a first filtered signal, which isamplified to provide a first amplified signal. The voltage or power ofthe first amplified signal is measured. The first amplified signal isfiltered, at a second filter, to pass a second band of frequenciesnarrower than the first band, to provide a second filtered signal. Thevoltage or power of the second filtered signal may be measured. A thirdfilter may be provided to filter the second filtered signal, to pass athird band of frequencies narrower than the second band, and to providea third filtered signal. If the measured voltage or power of the secondfiltered signal is less than a predetermined threshold, then the thirdfilter may be bypassed.

In some embodiments, an apparatus includes first and second receivermodules in a multiple input multiple output (MIMO) communicationssystem, first and second estimation circuits, and a state machine. Thefirst and second receiver modules are configured to process a firstinput signal and a second input signal, respectively Each receivermodule includes a first amplifier configured to amplify thecorresponding input signal, and a mixer coupled to the first amplifier,with the mixer configured to mix the amplified input signal outputted bythe first amplifier with an oscillator signal, to provide a mixedsignal. Each receiver module also includes a first filter configured tofilter the mixed signal to pass a first band of frequencies, a secondamplifier configured to amplify an output of the first filter, and asecond filter configured to filter the output of the second amplifier topass a second band of frequencies narrower than the first band. Thefirst estimation circuit is configured to measure voltage or power ofthe mixed signal of the first receiver module. The second estimationcircuit is configured to measure voltage or power at an output of thesecond amplifier of the first receiver module. The state machine iscoupled to the first and second estimation circuits. The state machineis configured to provide feedback to the first and second amplifiers ofthe second receiver module and to the mixer of the second receivermodule. The state machine is configured to increase a bias current of atleast one of the first amplifier of the second receiver module and themixer of the second receiver module, or decrease a gain of at least oneof the first amplifier of the second receiver module and the mixer ofthe second receiver module, or both increase the bias current anddecrease the gain, when the voltage or power measured by the firstestimation circuit is greater than a first predetermined threshold andthe voltage or power measured by the second estimation circuit is lessthan a second predetermined threshold. The state machine is furtherconfigured to decrease a gain of at least one of the first amplifier ofthe second receiver module, the second amplifier of the second receivermodule, and the mixer of the second receiver module when the voltage orpower measured by the second estimation circuit is greater than thesecond predetermined threshold. The apparatus may include a thirdestimation circuit configured to measure voltage or power at an outputof the second filter of the first receiver module. Each receiver modulemay includes a third filter configured to filter the output of thesecond filter of that receiver module to pass a third band offrequencies narrower than the second band. The state machine may befurther coupled to the third estimation circuit, and may be furtherconfigured to provide feedback to the third filter of the secondreceiver module. The state machine may be further configured to bypassthe third filter of the second receiver module when the voltage or powermeasured by the third estimation circuit is less than a thirdpredetermined threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

The following will be apparent from elements of the figures, which areprovided for illustrative purposes and are not necessarily to scale.

FIG. 1 is a block diagram of a receiver architecture known in the priorart.

FIG. 2 is a block diagram of a system architecture in accordance withsome embodiments of the present disclosure.

FIG. 3 is a depiction of selectivity to various filter outputs inaccordance with some embodiments.

FIG. 4A-C are depictions of various interference scenarios in accordancewith some embodiments.

FIG. 5 is a flow diagram of a process in accordance with someembodiments.

FIG. 6 is a flow diagram of a process in accordance with someembodiments.

FIG. 7 is a block diagram of a multiple input multiple output (MIMO)receiver architecture in accordance with some embodiments.

DETAILED DESCRIPTION

This description of the exemplary embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description.

Embodiments of the present disclosure provide a receiver architecture tooptimize receiver performance in the presence of interference. Invarious embodiments, estimation circuits are used with variableselectivity to determine the exact nature of the interference and tooptimize the performance correspondingly. The variable selectivity isachieved using stages of filtering with progressively narrowerbandwidths. Also, the actual method of optimizing the receiverperformance is an improvement compared to the prior art in that the gainsettings and the baseband filter order (stages to be used) will beoptimized based on the nature of the interference as determined by themeasurements from the estimation circuits.

FIG. 2 is a block diagram of a system architecture of a receiver 200 inaccordance with some embodiments of the present disclosure. An inputsignal 202 is received, e.g., from an antenna. The input signal is shownin differential form (RF_RX+ and RF_RX−); other signals in FIG. 2 may bein differential form but are not labeled as such, for visual clarity andto reduce clutter. The input signal is amplified by a low noiseamplifier (LNA) 204 to provide an amplified input signal 214. A localoscillator 210 generates one or more oscillator signals 212 (e.g.,sinusoids) based on control signals 208 from a synthesizer 206. A mixer216 mixes the amplified input signal 214 with the oscillator signal 212.The mixer may include 216 a and 216 b, one of which may process anin-phase component and one of which may process a quadrature component.Separate processing pathways are shown in FIG. 2 for the in-phase andquadrature components (with similar reference characters but differentsuffixes, “a” or “b”), but the processing is similar for each, so thediscussion below focuses on the top pathway in FIG. 2, which may be anin-phase or quadrature path. It is to be understood that the variousfeedback effects from state machine 254 to components such as filtersand amplifiers may apply to components in either the in-phase orquadrature path or using both.

Mixed signal 218 a provided by mixer 216 is processed by a series offilters 222 a, 232 a, 242 a, which may be baseband filters. Thesefilters implement the overall interference rejection of the baseband,and they may have programmable bandwidths with many different settings.For example, a multimode receiver may have bandwidths from 100 kHz up to10 MHz to support the various modes like Global System for Mobilecommunications (GSM), Time Division-Synchronous Code Division MultipleAccess (TD-SCDMA), Wideband Code Division Multiple Access (WCDMA), LongTerm Evolution (LTE), LTE-Advanced, and other communication standards asis known in the art. Also, the filters provide progressively morerejection as one moves further toward the output (toward the right sideof FIG. 2). The architecture also uses estimation circuits 220, 230, 240connected to the baseband outputs of the various stages as shown(labeled Pdet1, Pdet2, and Pdet3 for convenience). Estimation circuits220, 230, 240 may measure (estimate) power, e.g., by measuring voltageand computing power therefrom (because power and voltage are directlyrelated), and are referred to herein as power estimation circuits. Thesepower estimation circuits may be connected to either or both thein-phase and quadrature paths of the receiver. Also, these powerestimation circuits may be implemented as any kind of detector, e.g. apeak detector, power detector, or any other kind of power estimationcircuit as understood by one of ordinary skill in the art. Gainadjustment may be provided by a post-mixer amplifier (PMA) 226 a andvariable gain amplifier (VGA) 246 a.

Thus, mixed signal 218 is filtered by filter 222 a to provide signal 224a, which is amplified to provide signal 228 a. The amplified signal 228a is filtered to provide signal 234 a and then filtered to providesignal 244 a, which is amplified to provide signal 248 a. A logic module250 includes a received signal strength indication (RSSI) module 252,which measures power and provides an output 253 to an RF interferencemitigation state machine 254. RSSI 252 is described further below. Statemachine 254 receives inputs from power estimation circuits 220, 230, 240and from RSSI 252, and provides feedback to LNA 204, PMA 226 b, and VGA246. State machine 254 also may provide signals to the filters 222, 232,and/or 242 to enable one or more of the filters to be enabled asdiscussed further below. Logic module 250 may be coupled to atransmitter (not shown), which may provide a signal to an antenna fortransmission.

Filters 222 a, 232 a, and 242 a may provide progressively morerejection, as illustrated in FIG. 3. FIG. 3 shows that the various powerestimation circuits 220, 230, 240 will respond differently depending onthe frequency offset of any interference. For example, an interferencesignal far removed from the desired signal 310 in frequency will resultin a large detected power in Pdet1, but not in Pdet2 and Pdet3, due tothe baseband filtering. The term “desired signal” refers to the signaltransmitted by the transmitter and which, ideally, the receiver decodes.An adjacent channel signal will result in similar detected powerreadings in all three power estimation circuits 220, 230, 240. Frequencyresponses 320, 330, 340, and 350 in FIG. 3 may correspond to an outputof mixer 216, an output of filter 222 a, an output of filter 232 a, andan output of filter 242 a, respectively.

State machine 254, which may be a digital state machine that may beimplemented in various ways, controls circuitry in receiver 200 toperform power estimation and RSSI measurements, determine the optimumconfiguration for the RF circuits, and provide feedback accordingly.Such feedback may includes setting of the bandwidth of the variousfilters, possibly bypassing certain filter stages if not needed, and/ormodifying the gain and bias of the amplifier and/or mixer stages.

FIGS. 4A-C illustrate three different interference scenarios. Scenario1, shown in FIG. 4A, is an out of band interference case where thefrequency of interference signal 420 (fint) is relatively far away (outof band, denoted as foob) from the desired signal 410, i.e., fint>foob.Scenario 2, shown in FIG. 4B, is an intermediate interference case wherethe interference 430 is contained in a region below (lower in frequencythan) the out of band region but not in the adjacent channel, i.e.,fib1<fint<foob, where fib1 denotes an in-band limit. Scenario 3, shownin FIG. 4C, is an adjacent channel and/or proximate narrowbandinterference case. Interference 440 is at a lower frequency than fib1 inthis case. For each scenario, the power estimation circuits 220, 230,240 in FIG. 2 will respond differently, as described in the variouscases listed in Table 1 below. In Table 1, BBF1, BBF2, and BBF3 refer tofilters 222 a, 232 a, and 242 a, respectively (or filters 222 b, 232 b,and 242 b, respectively, if the lower processing path in FIG. 2 isapplicable).

TABLE 1 Cases for different regimes based on power measurementsInterference Pdet1 Pdet2 Pdet3 State Machine Case Region measurementmeasurement measurement Action Case 1 1 Pdet1 > Pdet2 < Pdet3 < LNA orMixer Bias threshold1 threshold2 threshold3 Increase and/or LNA and/orMixer gain decrease BBF2 and/or BBF3 may be bypassed Case 2 2 Pdet1 <Pdet2 > Pdet3 < BBF3 may be threshold1 threshold2 threshold3 bypassedCase 3 2 Pdet1 > Pdet2 > Pdet3 < LNA and/or Mixer threshold1 threshold2threshold3 gain decrease BBF3 may be bypassed Case 4 3 Pdet1 < Pdet2 >Pdet3 > PMA gain decreased threshold1 threshold2 threshold3 All filtersenabled Case 5 3 Pdet1 > Pdet2 > Pdet3 > LNA and/or Mixer threshold1threshold2 threshold3 gain decrease All filters enabled

State machine 254 directs power estimators 220, 230, 240 to performpower estimation measurements, and based on the measurements, employslogic according to the relevant case. The thresholds threshold1,threshold2, and threshold3 may be predetermined and form the basis forcomparisons as shown in Table 1.

By employing progressively narrower filters and comparing powermeasurements at one stage relative to another in a differential manner,embodiments of the present disclosure identify the region ofinterference and may intelligently take action accordingly (throughstate machine 254) to mitigate such interference. Such processing isdynamic, enabling efficient adaptation to various interferenceconditions, and is not pre-wired like prior art approaches that maydegrade performance unnecessarily due to flawed assumptions aboutinterference.

For these five different cases, the radio circuits may be configuredoptimally in a manner that varies from nominal operation as follows.Nominal operation may include enabling all three baseband filters 222 a,232 a, 242 a (or filters 222 b, 232 b, 242 b for the lower processingpath of FIG. 2), and employing predetermined gain settings that maximizethe receiver's signal to noise ratio (SNR). In the discussion below ofthe various cases, only components in the upper processing path of FIG.2, with suffix“a” (e.g., filter 222 a) are discussed for brevity, but itis understood that the corresponding component(s) in the lowerprocessing path (with suffix “b”) are applicable if the lower processingpath is used.

In case 1, state machine 254 may send feedback that results in bypassingfilters 242 a and/or 232 a. A bias current of LNA 204 and/or of mixer216 may be increased, or a gain of LNA 204 and/or of mixer 216 may bedecreased, or both the bias current may be increased and the gaindecreased, to improve the linearity of the RF stages.

In case 2, filter 242 a may be bypassed or disabled when the powermeasured at power estimation circuit 240 is less than a predeterminedthreshold. Gain of PMA 226 a may be decreased to improve linearity ofthe receiver.

In case 3 filter 242 a may be bypassed or disabled when the powermeasured at power estimation circuit 240 is less than a predeterminedthreshold. Gain of LNA 204 and/or of mixer 216 may be decreased toimprove the linearity of the receiver.

In case 4, all three baseband filters 222 a, 232 a, 242 a may beenabled. Gain of PMA 226 a may be decreased to improve linearity of thereceiver.

In case 5, all three baseband filters 222 a, 232 a, 242 a may beenabled. Gain of LNA 204 and/or of mixer 216 may be decreased to improvelinearity of the receiver.

State machine 254 may send signals 260 a, 260 b, 260 c instructing theuse of various numbers of filters as specified in the cases above.

In some embodiments, periodically, after the operation of the receiveris modified, the power estimation readings for the nominal operationcase may be rechecked to determine the new optimal configuration. Thus,this architecture allows the optimal operation to change dynamicallywith changing interference conditions. The periodicity may beconstrained by certain factors. On the minimum side, the minimumperiodicity may be determined by the ability of the power estimationcircuits to perform actual measurements (e.g., 10 μsec to hundreds ofμsec) and the typical slot size for cellular communication systems.Several parameters such as gain are often held constant during a slot toensure good quality signal without excessive transients during the slot.Based on these two constraints, the minimum periodicity of the statechange may be on the order of a slot length or approximately 500-700μsec. On the maximum side, the periodicity might be dictated by theslowest expected variation of signal conditions for a device such as acellular phone. This can be calculated from the Doppler shift due to a 2GHz carrier travelling at pedestrian speeds of, e.g., 3 km/hr to beabout 100 msec. Therefore, on the high end the periodicity may beapproximately 100 msec.

One factor that may determine the periodicity of the operation is achannel quality metric such as signal to noise ratio (SNR) estimation orblock level error rate (BLER). Channel quality metrics such as SNRestimation and block level error rate may be calculated at a channelquality estimator 272 in logic module 250. These metrics are estimatedusing the techniques applicable in a typical cellular standard, as isunderstood by one of ordinary skill in the art. A typical approach forcalculating block error rate is to perform cyclic redundancy checks onblocks of bits and calculating a running total of the ratio of blocksthat fail this check to the total number of blocks received. Thesemetrics may be measured continually at channel quality estimator 272 andmay indicate whether the signal conditions are poor, which may indicatethat interference is present and thus should be evaluated morefrequently. Thus, in some embodiments, operation proceeds with thelowest rate until a quality metric exceeds a predetermined threshold.When this happens, the updates may become more frequent based on logicand control at a rate update logic module 270 of logic module 250. Anumber of thresholds may be predetermined that set operation in, e.g., ahigh update rate, medium update rate, and slow update rate depending onthe signal conditions.

Example Filter Parameters

The baseband filter stages may be implemented in various ways to provideprogressively narrower bandwidths. For example, filter 222 a may beimplemented as a 1 pole filter, filter 232 a may be implemented as a 4pole/2 zero filter, and filter 242 a may be implemented as a 2 pole/2zero filter.

A number of different interference regions, e.g., three interferenceregions, may be the basis for operation in different modes. A breakdownof interference regions may be as follows. Interference region 3 maycorrespond to any signal that is more than eight times the channelbandwidth away in frequency from a desired signal. Interference region 2may correspond to any signal that is between around two times thechannel bandwidth and eight times the channel bandwidth away infrequency. Interference region 1 may correspond to any signal around onetimes the channel bandwidth away in frequency, i.e., the adjacentchannel. This breakdown results in the following interference regionsshown in Table 2 for different common communications standards.

TABLE 2 Interference regions for various communications standardsInterference Interference Interference Standard Channel BW Region 1Region 2 Region 3 GSM/Edge 200 kHz   200 kHz offset   400 kHz to 1.6MHz >1.6 MHz  TD-SCDMA 1.6 MHz   1.6 MHz offset    3.2 MHz to 12.8MHz >12.8 MHz   LTE (3 MHz) 3 MHz 3 MHz offset  6 MHz to 24 MHz >24 MHzWCDMA 5 MHz 5 MHz offset 10 MHz to 40 MHz >40 MHz LTE (5 MHz) 5 MHz 5MHz offset 10 MHz to 40 MHz >40 MHz

The filters 222 a, 232 a, 242 a may be described in terms of the amountof rejection in the three interference regions. Some exemplary numbersfor the rejection for each filter are shown in Table 3.

TABLE 3 Rejection for various filters Interference Filter InterferenceRegion 1 Interference Region 2 Region 3 Filter 222a  8 dB 20 dB 25 dBFilter 232a 20 dB 50 dB 70 dB Filter 242a 20 dB 30 dB 50 dB

As an example, suppose it is desired to detect interference of >−30 dBm.Then, power estimation thresholds for the power estimation circuits maybe set as follows: threshold for Pdet1=−35 dBm, threshold for Pdet2=−52dBm, and threshold for Pdet3=−70 dBm. The “Yes” and “No” designationsbelow (determined by state machine 254) in Tables 4-6 indicate whetherthe corresponding suggested threshold is exceeded for the particularpower estimation circuit.

TABLE 4 Example for signal in interference region 3 with power = −30 dBmPower measurement referenced to antenna Logic related to threshold Pdet1= −30 dBm >−35 dBm—Yes Pdet2 ≦−55 dBm >−52 dBm—No Pdet3 ≦−125 dBm >−70dBm—No

TABLE 5 Example for signal in interference region 2 with power = −30 dBmPower measurement referenced to antenna Logic related to threshold Pdet1= −30 dBm >−35 dBm—Yes Pdet2 ≧−50 dBm >−52 dBm—Yes Pdet3 = −100 dBm >−70dBm—No

TABLE 6 Example for signal in interference region 1 with power = −30 dBmPower measurement referenced to antenna Logic related to threshold Pdet1= −30 dBm >−35 dBm—Yes Pdet2 ≧−38 dBm >−52 dBm—Yes Pdet3 = −58 dBm >−70dBm—Yes

Thus, embodiments of the present disclosure may determine that aninterference signal is present with >−35 dBm power and may identifywhich frequency region the interference inhabits. This is just onescenario and many other possible detection levels, methods, and offsetsare possible.

State machine 254 may send signals 260 d, 260 e, 260 f, 260 g to adjustgain and/or bias of various system components as shown in FIG. 2. Thereceiver architecture may include an LNA, mixer, and local oscillator(LO) chain that drives the mixer as shown in FIG. 2. In a typical case,the linearity of the RF circuits may be evaluated using the 1 dBcompression point metric. This metric indicates the point at which thecircuits become compressed and therefore is the maximum interferencelevel that can be allowed for good quality reception. The 1 dBcompression point may be determined either by the biasing of thetransistors used in the LNA and mixer or by the amount of bias used inthe LO chain depending on the architecture of the circuits. In a typicalcase, the 1 dB compression point may be adjusted to be around −30 dBm inorder to save current. If interference is detected to be >−30 dBm, thena typical change in bias current of 5-10 mA may provide a 10 dB increasein 1 dB compression point to be >−20 dBm.

Alternatively, a gain change may be implemented to achieve the increasein the 1 dB compression point. For example, if the circuits are operatedin a low bias condition with a 1 dB compression point around −30 dBm,then a 10 dB reduction in gain may increase the compression pointto >−20 dBm. Thus, some embodiments may include a 5-10 dB gain changethat increases the 1 dB compression point of the RF circuits by theequivalent 5-10 dB. A gain change combined with a bias change mayprovide an increase in 1 dB compression point of between 15 and 20 dB.

A factor that may determine whether to improve the linearity with a gainand/or bias change is the received signal strength indication (RSSI)provided by RSSI module 252. The improvement in linearity using a gainchange also degrades the signal to noise performance since the noisefigure of the RF circuits is increased. Because of this, someembodiments may use an RSSI threshold to determine at what point a gainchange is to be used. In some embodiments, this RSSI threshold sets alevel that must be exceeded before a gain change will be used to improvethe linearity. In general, however, since the gain change method usesreduced bias and therefore less current drain, if the RSSI threshold isexceeded, a gain change is used rather than a bias change.

FIG. 5 is a flow diagram of a process 500 in accordance with someembodiments. After process 500 begins, an input signal (e.g., signal202) is amplified (block 510), to provide an amplified input signal(e.g., signal 214), which is mixed (block 520) with an oscillator signal(e.g., signal 212), to provide a mixed signal (e.g., signal 218 a). Thevoltage or power of the mixed signal is measured (block 530), e.g., atPdet1 shown in FIG. 2. The mixed signal is filtered (block 540), at afirst filter, to pass a first band of frequencies, to provide a firstfiltered signal (e.g., signal 224 a), which is amplified (block 550) toprovide a first amplified signal (e.g., signal 228 a). The voltage orpower of the first amplified signal is measured (block 560), e.g., atPdet2 shown in FIG. 2. The first amplified signal is filtered (block570), at a second filter, to pass a second band of frequencies narrowerthan the first band, to provide a second filtered signal (e.g., signal234 a). If the measurement at Pdet1 is greater than a predeterminedthreshold T1 and the measurement at Pdet2 is less than a predeterminedthreshold T2 (comparison 572), then a gain used for the amplifying theinput signal, or for the mixing, or for both, may be decreased, or abias current used for the amplifying the input signal, or for themixing, or for both, may be increased. Based on an RSSI measurement,which may be computed at RSSI module 252 in FIG. 2, and a comparisonwith an RSSI threshold (comparison 574), gain may be decreased or biascurrent may be increased as shown in FIG. 5 (blocks 580, 582). If themeasurement at Pdet2 is greater than the predetermined threshold T2(comparison 576), then a gain used for at least one of the amplifyingthe first filtered signal, the amplifying the input signal, and themixing may be decreased (block 584).

State machine 254 may provide feedback via signal 260 a to vary the gainof VGA 246 a. The gain change may offset any gain changes in the LNA204, mixer 216, and/or PMA 226 b. A gain change in the VGA 246 a willgenerally not improve the linearity of the receiver with interferencesince this VGA stage is after all the filter stages. However, if thegain of the LNA, mixer, and/or PMA is changed in order to improve thelinearity, the gain of the VGA may be adjusted to compensate for thereduction of gain in those stages.

The receiver architecture of FIG. 2 may also be implemented efficientlyfor a MIMO (multiple input multiple output) system as shown in FIG. 7.Because of the MIMO requirements for 3G and 4G cellular systems, adiversity receiver is often included in the RF and basebandarchitecture. This additional receiver is not needed for GSM/Edge modeand therefore may be used to perform the power estimation functionalityshown in FIG. 2. Based on this information and other factors describedabove (e.g., regarding various cases and interference regions), the modeof the receiver(s) may be optimally configured based on the determinedinterference level and/or the frequency of the interference.

FIG. 6 is a flow diagram of a process 600 in accordance with someembodiments. After process 600 begins, an input signal (e.g., signal202) is amplified (block 610), to provide an amplified input signal(e.g., signal 214), which is mixed (block 612) with an oscillator signal(e.g., signal 212), to provide a mixed signal (e.g., signal 218 a). Thevoltage or power of the mixed signal is measured (block 614), e.g., atPdet1 shown in FIG. 2. The mixed signal is filtered (block 616), at afirst filter (e.g., filter 222 a), to pass a first band of frequencies,to provide a first filtered signal (e.g., signal 224 a), which isamplified (block 618) to provide a first amplified signal (e.g., signal228 a). The voltage or power of the first amplified signal is measured(block 620), e.g., at Pdet2 shown in FIG. 2. The first amplified signalis filtered (block 622), at a second filter (e.g., filter 232 a), topass a second band of frequencies narrower than the first band, toprovide a second filtered signal (e.g., signal 234 a). The voltage orpower of the second filtered signal is measured (block 624). A thirdfilter (e.g., filter 242 a) is provided (block 626) to filter the secondfiltered signal, to pass a third band of frequencies narrower than thesecond band, and to provide a third filtered signal. If the measuredpower of the second filtered signal is less than a predeterminedthreshold, then the third filter is bypassed (block 628). In otherwords, the third filter is disabled when a predetermined condition ismet (when the measured voltage or power of the second filtered signal isless than a predetermined threshold).

FIG. 7 shows a receiver module 710 b, which may receive an input from aprimary receive antenna 712 b, and a receiver module 710 a, which mayreceive an input from a diversity antenna 712 a. Processing in each ofthe receiver modules is similar to processing discussed above in thecontext of FIG. 2, and only certain differences from FIG. 2 arediscussed below. The diversity receiver module 710 a may be used forpower estimation at power estimation circuits 720 (labeled Pdet1), 730(Pdet2), 740 (Pdet3). State machine 754 may provide feedback signals asshown in FIG. 7, to control the use of filters, gain, and/or biascurrents in a manner similar to that described above.

The use of the diversity receiver in some embodiments to performinterference estimation in parallel provides several advantages. Oneadvantage is that the diversity receiver can be adjusted to anybandwidth option that is desired at any time in order to detectinterference. The primary receiver is tasked with receiving the desiredsignal and therefore the baseband filters have limited bandwidth duringthe desired reception slot to limit noise and interference. Thediversity receiver, when used for interference detection, has no suchlimitation, so the bandwidth can be increased as desired. Anotheradvantage is that the diversity receiver gain may be adjusted for thebest performance to check the interference without considering thedesired signal. The primary receiver must receive the desired signal andtherefore the gain control is set to optimize the level of that signal.The diversity receiver, when used for interference detection, is againnot constrained by the need to receive the desired signal, and thereforethe gain may be optimized to detect interference.

Although examples are illustrated and described herein, embodiments arenevertheless not limited to the details shown, since variousmodifications and structural changes may be made therein by those ofordinary skill within the scope and range of equivalents of the claims.

What is claimed is:
 1. A method comprising: amplifying an input signalto provide an amplified input signal; mixing the amplified input signalwith an oscillator signal, to provide a mixed signal; measuring voltageor power of the mixed signal; filtering the mixed signal, at a firstfilter, to pass a first band of frequencies, to provide a first filteredsignal; amplifying the first filtered signal, to provide a firstamplified signal; measuring voltage or power of the first amplifiedsignal; filtering the first amplified signal, at a second filter, topass a second band of frequencies narrower than the first band, toprovide a second filtered signal; decreasing a gain used for at leastone of the amplifying the input signal and the mixing, when the measuredvoltage or power of the mixed signal is greater than a firstpredetermined threshold and the measured voltage or power of the firstamplified signal is less than a second predetermined threshold; anddecreasing a gain used for at least one of the amplifying the firstfiltered signal, the amplifying the input signal, and the mixing, whenthe measured voltage or power of the first amplified signal is greaterthan the second predetermined threshold.
 2. The method of claim 1,wherein decreasing the gain used for at least one of the amplifying thefirst filtered signal, the amplifying the input signal, and the mixingcomprises decreasing the gain used for amplifying the first filteredsignal, when the measured voltage or power of the mixed signal is lessthan the first predetermined threshold and the measured voltage or powerof the first amplified signal is greater than the second predeterminedthreshold.
 3. The method of claim 1, wherein decreasing the gain usedfor at least one of the amplifying the first filtered signal, theamplifying the input signal, and the mixing comprises decreasing thegain used for at least one of the amplifying the input signal and themixing, when the measured voltage or power of the mixed signal isgreater than the first predetermined threshold and the measured voltageor power of the first amplified signal is greater than the secondpredetermined threshold.
 4. The method of claim 1, further including:measuring voltage or power of the second filtered signal; providing athird filter to filter the second filtered signal, to pass a third bandof frequencies narrower than the second band, and to provide a thirdfiltered signal; and bypassing the third filter when the measuredvoltage or power of the second filtered signal is less than a thirdpredetermined threshold.
 5. The method of claim 1, further including:measuring voltage or power of the second filtered signal; and filteringthe second filtered signal to pass a third band of frequencies narrowerthan the second band, to provide a third filtered signal; whereindecreasing the gain used for at least one of the amplifying the firstfiltered signal, the amplifying the input signal, and the mixingcomprises decreasing the gain used for amplifying the first filteredsignal, when the measured voltage or power of the mixed signal is lessthan the first predetermined threshold and the measured voltage or powerof the second filtered signal is greater than a third predeterminedthreshold.
 6. The method of claim 5, further including: amplifying thethird filtered signal to provide a second amplified signal; measuringvoltage or power of the second amplified signal; and determining whetherthe measured voltage or power of the second amplified signal exceeds apredetermined received signal strength indication (RSSI) threshold;wherein the decreasing the gain used for the at least one of theamplifying the input signal and the mixing is responsive to adetermination that the measured voltage or power of the second amplifiedsignal exceeds the predetermined RSSI threshold.
 7. The method of claim1, further including: measuring voltage or power of the second filteredsignal; and filtering the second filtered signal to pass a third band offrequencies narrower than the second band, to provide a third filteredsignal; wherein decreasing the gain used for at least one of theamplifying the first filtered signal, the amplifying the input signal,and the mixing comprises decreasing the gain used for at least one ofthe amplifying the input signal and the mixing, when the measuredvoltage or power of the mixed signal is greater than the firstpredetermined threshold and the measured voltage or power of the secondfiltered signal is greater than a third predetermined threshold.
 8. Themethod of claim 7, further including: amplifying the third filteredsignal to provide a second amplified signal; measuring voltage or powerof the second amplified signal; and determining whether the measuredvoltage or power of the second amplified signal exceeds a predeterminedreceived signal strength indication (RSSI) threshold; wherein thedecreasing the gain used for the at least one of the amplifying theinput signal and the mixing is responsive to a determination that themeasured voltage or power of the second amplified signal exceeds thepredetermined RSSI threshold.
 9. A method comprising: amplifying aninput signal to provide an amplified input signal; mixing the amplifiedinput signal with an oscillator signal, to provide a mixed signal;measuring voltage or power of the mixed signal; filtering the mixedsignal, at a first filter, to pass a first band of frequencies, toprovide a first filtered signal; amplifying the first filtered signal,to provide a first amplified signal; measuring voltage or power of thefirst amplified signal; filtering the first amplified signal, at asecond filter, to pass a second band of frequencies narrower than thefirst band, to provide a second filtered signal; and decreasing a gainused for at least one of the amplifying the input signal and the mixing,when the measured voltage or power of the mixed signal and the measuredvoltage or power of the first amplified signal satisfy a predeterminedcondition.
 10. The method of claim 9, wherein the predeterminedcondition is that the measured voltage or power of the mixed signal isgreater than a first predetermined threshold and the measured voltage orpower of the first amplified signal is less than a second predeterminedthreshold.
 11. The method of claim 9, further including: decreasing thegain used for amplifying the first filtered signal, when the measuredvoltage or power of the mixed signal is less than a first predeterminedthreshold and the measured voltage or power of the first amplifiedsignal is greater than a second predetermined threshold.
 12. The methodof claim 9, further including: decreasing the gain used for at least oneof the amplifying the input signal and the mixing, when the measuredvoltage or power of the mixed signal is greater than a firstpredetermined threshold and the measured voltage or power of the firstamplified signal is greater than a second predetermined threshold. 13.The method of claim 9, further including: measuring voltage or power ofthe second filtered signal; providing a third filter to filter thesecond filtered signal, to pass a third band of frequencies narrowerthan the second band, and to provide a third filtered signal; andbypassing the third filter when the measured voltage or power of thesecond filtered signal is less than a predetermined threshold.
 14. Amethod comprising: amplifying an input signal to provide an amplifiedinput signal; mixing the amplified input signal with an oscillatorsignal, to provide a mixed signal; measuring voltage or power of themixed signal; filtering the mixed signal, at a first filter, to pass afirst band of frequencies, to provide a first filtered signal;amplifying the first filtered signal, to provide a first amplifiedsignal; measuring voltage or power of the first amplified signal;filtering the first amplified signal, at a second filter, to pass asecond band of frequencies narrower than the first band, to provide asecond filtered signal; and decreasing a gain used for at least one ofthe amplifying the first filtered signal, the amplifying the inputsignal, and the mixing, when the measured voltage or power of the firstamplified signal satisfies a predetermined condition.
 15. The method ofclaim 14, wherein the predetermined condition is that the measuredvoltage or power of the first amplified signal is greater than thesecond predetermined threshold.
 16. The method of claim 14, furtherincluding: decreasing a gain used for at least one of the amplifying theinput signal and the mixing, when the measured voltage or power of themixed signal is greater than a first predetermined threshold and themeasured voltage or power of the first amplified signal is less than asecond predetermined threshold.
 17. The method of claim 14, furtherincluding: measuring voltage or power of the second filtered signal;providing a third filter to filter the second filtered signal, to pass athird band of frequencies narrower than the second band, and to providea third filtered signal; and bypassing the third filter when themeasured voltage or power of the second filtered signal is less than apredetermined threshold.
 18. The method of claim 14, wherein decreasingthe gain used for at least one of the amplifying the first filteredsignal, the amplifying the input signal, and the mixing comprisesdecreasing the gain used for amplifying the first filtered signal, whenthe measured voltage or power of the mixed signal is less than a firstpredetermined threshold and the measured voltage or power of the firstamplified signal is greater than a second predetermined threshold. 19.The method of claim 14, wherein decreasing the gain used for at leastone of the amplifying the first filtered signal, the amplifying theinput signal, and the mixing comprises decreasing the gain used for atleast one of the amplifying the input signal and the mixing, when themeasured voltage or power of the mixed signal is greater than a firstpredetermined threshold and the measured voltage or power of the firstamplified signal is greater than a second predetermined threshold.